Many mobile devices include a both a primary antenna and a diversity antenna to support communications over each antenna, thereby improving the quality of the communications to and from the mobile device. However, if the primary and diversity antennas are located in close proximity to one another, the two antennas couple with one another causing the signals transmitted by one of the antennas with be sensed by the other antenna. Due to this coupling, the communications at the other antenna are degraded (sometimes referred to as de-sensed). Accordingly, mobile device designers tend to physically separate the primary and diversity as much as possible to reduce the coupling between the primary and diversity antennas.
However, as mobile devices have grown smaller while including ever more components, it has become more and more difficult to physically separate the primary and diversity antennas. Thus, while physical separation can somewhat decouple the primary and secondary antennas, additional techniques are needed to mitigate the impact the effects of coupling between the primary and diversity antennas.
Further, many communication systems now involve carrier aggregation (CA) techniques to improve communication throughput. CA can be implemented by either utilizing time-division duplexing (TDD) that segregates the uplink and downlink to different time slots of the same carrier (e.g., frequency) or by utilizing frequency-division duplexing (FDD) where the uplink and downlink signals are communicated simultaneously using different component carriers. Due to the simultaneous nature of FDD communications and the above-described coupling effects, signals transmitted by the primary antenna are sensed at the diversity antenna. Said another way, the signals transmitted by the primary antenna jam the diversity antenna from properly being able to receive other signals. It should be noted that this de-sensing still occurs in TDD systems, albeit to a lesser extent than FDD systems.
Conventional solutions have relied upon filtering techniques that filter out the carrier(s) associated with the primary antenna. However, for some combinations of uplink carriers and downlink carriers, the harmonics associated with the uplink carrier (and/or the intermodulation distortion harmonics associated with the composite CA transmit signal) fall within the frequency band that includes the downlink carriers associated with the diversity antenna. Accordingly, traditional filtering techniques cannot filter out the harmonics associated with the uplink carrier without also filtering out the downlink carrier associated with the diversity antenna.